As part of our ongoing studies of dual site ruthenium and boron-containing catalysts for the manipulation of hydride groups, we have recently reported a series of [di(pyridyl)borate]ruthenium complexes (1, 2)1 that exhibit remarkable reactivity in a number of applications,2 notably including dehydrogenation of ammonia borane.3 Although they are successful catalysts, these di(pyridyl)dimethylborate-derived complexes are cumbersome to prepare, due largely to dependence on an expensive and reactive BrBMe2 starting material and high water and oxygen sensitivity of intermediate complexes in their syntheses. Further, despite their catalytic utility, no direct evidence has been collected to give a mechanistic account of the cooperative role, if any, that boron and ruthenium play in the reactive mechanisms of 1 or 2.4 We suspect this is partially due to the robustness of the bridging μ-OH ligand between the boron and ruthenium centers in 2, which inhibits access to a free borane in catalytic reactions (FIG. 1).
Accordingly, there is a need to develop a strategy to overcome each of these limitations and introduce a new synthesis of primary amines from nitriles.